WASHINGTON (CNN) -- The United Nations and the Red Cross began distributing relief supplies Tuesday to people affected by the devastating cyclone that killed at least 22,000 people in Myanmar on Friday.
The first relief delivered -- water, plastic sheeting, clothing and insecticide-treated bed nets -- came from stocks that were already in the country. Aid agencies abroad are struggling to transport supplies into Myanmar and to the neediest areas.
The head of the Association of Southeast Asian Nations called on members states to send aid to Myanmar -- traditionally known as Burma -- saying, "Given the frequency of such major natural disasters, ASEAN must ... intensify efforts in disaster management and emergency response."
UNICEF deployed 130 workers to distribute medicine for 155,000 people, water purifying solution, oral rehydration salts, tarps, bleach and family kits that include cooking and cleaning tools and jerry cans.
Lack of clean water and poor sanitation in the wake of the disaster increases the risk of diarrhea, especially for children. Floods can drive mosquito breeding, leading to outbreaks of malaria and dengue fever, according to UNICEF.
"Time is of the essence," UNICEF Executive Director Ann Veneman said. "In situations such as these, children are highly vulnerable to disease and hunger, and they need immediate help to survive."
President Bush joined a chorus of international leaders urging Myanmar's reclusive military government to allow the flow of aid. "Let the United States come and help you," Bush exhorted the junta on Tuesday.
The U.S. pledged $3.25 million and has promised to send Navy ships in the region to help if Myanmar's government requests it. Watch how politics plays into disaster relief »
Relief workers are relying on helicopters to distribute supplies, the World Health Organization said in a statement.
"This is proving slow and relatively inefficient. Clearing roads is a high priority in order to move supplies urgently to the population in need," the WHO said.
"The storm and a large tidal wave that traveled up the Irrawaddy River have flooded many roads, which make access to the affected area very difficult," said John Sparrow, a spokesman for the International Federation of Red Cross and Red Crescent Societies. "The infrastructure of the region has been severely affected."
Much of the country is without electricity, communications and transportation, according to Myanmar state radio and opposition sources.
The cyclone is the deadliest natural disaster to hit Myanmar in recorded history, according to a U.N.-funded disaster database that includes figures from the past century. Learn more about Myanmar »
"The situation is very bad and not getting better," Shari Villarosa, the top U.S. diplomat in Myanmar, said Tuesday.
The World Food Programme handed out rice Tuesday in Yangon, the nation's main city. The organization indicated that the rice was the first of 8,000 metric tons of WFP food stocks available in the country.
But food is not the top priority for victims at the moment, said Richard Horsey, spokesman for the U.N. Office for the Coordination of Humanitarian Affairs said.
"Right now, water is much more important, and shelter," he said.
The Office of the United Nations High Commissioner for Refugees focused on shelter, purchasing $50,000 of basic supplies, including emergency tarpaulins, plastic sheeting and canned food. The agency said it was "emptying" stockpiles of tents and plastic sheeting in neighboring Thailand for urgent dispatch to Myanmar.
The supplies should be enough for 10,000 people, the agency said, and will be distributed through a disaster management committee that has been established by the Myanmar government.
The Myanmar Red Cross handed out relief supplies, such as clean drinking water, plastic sheeting, clothing, insecticide-treated bed nets to help prevent malaria, and kitchen items, the International Federation of Red Cross and Red Crescent Societies said. The groups also sent a round of shelter kits from Kuala Lumpur and released $189,000 to support the Red Cross' effort.
Countries from China to the Netherlands have pledged aid. Thailand and Indonesia are using military transport planes to deliver supplies. Watch the world scramble to help »
The U.S. Navy is making preparations to respond to any requests for assistance, U.S. military officials said. The Navy has calculated that it would take its nearest ships four days to get to the affected area. Watch how the Navy could help »
Myanmar's military junta is subject to international sanctions. Its most famous pro-democracy activist, Aung San Suu Kyi, is under house arrest.
Bush's statement on Myanmar came as he signed legislation awarding the Congressional Gold Medal to Suu Kyi "in recognition of her courageous and unwavering commitment to peace, nonviolence, human rights and democracy in Burma." Watch Bush honor Suu Kyi and pressure the junta »
Australian Foreign Minister Stephen Smith said it is important not to let politics interfere with aid.
"We very strongly disagree with the regime in Burma but we have over the years contributed humanitarian assistance directly to the people of Burma, and given the devastation that occurred, we have already made it clear that we stand ready to provide humanitarian assistance," Smith said.
A key United Nations agency said Tuesday that simply getting visas for aid workers to enter Myanmar is the greatest challenge facing international aid organizations trying to bring relief into the cyclone-ravaged country. See the storm's track »
Visas are available only through the foreign ministry in Yangon, the United Nations Joint Logistics Center said in a statement.
The government of Myanmar has not officially endorsed international assistance, the UNJLC added, but said Myanmar "is willing to accept international assistance, preferably bilateral, government to government."
CNN Pentagon correspondent Barbara Starr contributed to this report.